The present disclosure relates to image forming apparatuses using an electrophotographic system such as copiers, printers, facsimiles and multifunction peripherals of these devices. More specifically, the present disclosure relates to an image carrier unit in which an image carrier and a charging device for charging the image carrier are unitized, as well as to an image forming apparatus including the image carrier unit.
In image forming apparatuses, conventionally, a charging device is used to electrically charge the surface of a photosensitive drum, which is an image carrier. Two types of charging devices are known, one being the corona charging system in which with a photosensitive drum and a corona wire disposed out of contact therebetween, the surface of the photosensitive drum is electrically charged by corona discharge, and the other being the contact charging system in which a charging roller or other charging member is brought into contact with the surface of the photosensitive drum to charge the surface. However, in recent years, for reduction of emission amounts of ozone, which is harmful to the human body, the contact charging system involving less ozone emission has been being adopted increasingly.
Such charging devices as described above are in many cases provided as unitized with a photosensitive drum into an image carrier unit. For example, the charging device is made fittable to and removable from the unit main body so as to facilitate maintenance, replacement or the like of the charging device.
In the contact charging system, when a charging roller is put into contact with the surface of the photosensitive drum, foreign matters such as toner and paper dust of sheets may stick onto the surface of the photosensitive drum and then move to the outer peripheral surface of the charging roller. Foreign matters sticking to the outer peripheral surface of the charging roller give rise to charging failures on the surface of the photosensitive drum, making a cause of large influences on image quality.
Accordingly, there has been proposed a structure including a cleaning member for cleaning the charging roller. For example, a charging device is known which includes: a support member for rotatably supporting a charging roller and moreover rotatably and axially-reciprocatably supporting a cleaning member; a disc-shaped cam member which is provided on a rotating shaft of the cleaning member and which is inclined by a specified angle from a direction perpendicular to the axial direction; and a guide member provided inside the housing. As the cleaning member is rotated, the cam member is guided by the guide member so that the cleaning member with the cam member provided thereon is reciprocatively moved along the axial direction in accordance with the inclination of the cam member. As a result of this, the outer peripheral surface of the charging roller is cleaned.